Apparatus for electrical separation of suspended particles from gases



. Nov. 22, 1927.`

E y E. ANDERSON APPARATUS FOR ELECTRICAL SEPARATION OF SUSPENDEDPARTICLES FROM GASES Filed Sept. 1'7 1925 Hg. z

INVENTOR dersbn Y, ATT' NEY n A P m 5W Y, B

Patented Nov. 22, 1927.

UNITED STATES 1,650,105 PATENT OFFICE.

EVALD ANDERSON, OF ALHAMBRA, CALIFORNIA, ASSIGNOR TO INTERNATIONAL PRE-CIPITATION COMPANY, OF LGS ANGELES, CALIFORNIA, A CORPORATION Oil?vCALI- FORN IA.

APPARATUS FOR ELECTRICAL SEPARATION OF SUSPENDED PARTICLES FROM GASES.

Application led September 17, 1925i Serial No. 57,011.

This invention relates to apparatus for separation of suspendedparticles from gases by electrical action and particularly to the formof such apparatus in which the gases containing the particles are passedbetween electrodes maintained at a high potential dierence and soconstructed as to produce an electrical discharge from certain of saidelectrodes, resulting in charging of the suspended particles and thedeposition of charged particles on the electrodes and particularly enthe electrodes opposing the discharge electrodes.

The main object of thek present invention is to provide dischargeelectrodes of such construction as to improve the operation of theelectrical precipitator, and particularly of such character as tomaintain a highly" uniform distribution of the electrical dischargethroughout the body of the gas being treated so as to'result in a morecomplete and eflicient precipitation of the suspended matter, and alsoto prevent arcing or disruptive discharge between the electrodes.

In electrical precipitators there is a tendency for concentration of theelectrical discharge at certain portions of the electrodes leading tocertain disadvantageous results. By reason of such concentration of theelectricl discharge insuch portions of the-electrodes there is liable tobe a large portion of the gas being treated which is not subjected tothe action of such electrical discharge and consequently such portionsof the gas may pass through the electrical precipitator' without beingsubjected effectively to the electrical precipitating action. In orderto ensure contact of all portions of the gas with the electricaldischarge it has generally been necessary to make the gas velocityextremely slow or to make Athe conduit or gas treating space betweenrthe electrodes suiciently long to ensure that all of the gas will besubjected to electrical action at some time in its passage through suchspace.

Furthermore, by reason of such concentral tion of electrical dischargethere is liable to be breaking down of the dielectric resistance of thegas to such an extent as to cause arcing or disruptive discharge which.seriously decreases the eiiciency of the treater by limiting thepotential difference which may be maintained between the electrodes,

and by otherwise interfering with the operation of the precipitator.

I have found that by covering the discharge electrodes, which generallycomprise ne wires or rods of smalldiameter, with suitablesemi-conducting material so as to interpose a considerable resistance tothe passage of current, concentration of the electrical discharge at anyone portion or at arelatively limited number of portions ofthe dischargeelectrodes may be prevented. This may be considered as being due to thefact that the relatively'high resistance of the semi-conducting coatingon the surface of the discharge electrode prevents the passage of anexcessive amount of current at any one point and particularly actsvtoprevent the passage of such a large amount of current as would otherwiseresult upon breaking down of the dielectric resistance of the gas andthus cause arcing or disruptive discharge as above described. Adischarge electrode of this character may be employed in connection witha collecting electrode of semi-conducting or high resistance material,for eXample,as described in my Patent No. 1,541,677, dated June 9, 1925,

'or in connection with collecting electrodes of metal. In the first caseit will be seen that in addition to the air gaptwo layers ofsemiconducting material are interposed between the high tension and lowtension sides of the precipitator, one surrounding the dischargeelectrode and the other at the collecting electrode while in the secondcase only the semi-conducting layer surrounding, the discharge.electrode is interposed.

The accompanying drawings illustrateembodiments of my invention andreferring thereto:

Fig. 1 isa vertical'transverse section of one form of my invention.

Fig. 2 is a section on line 2-2 in Fig. 1.

Fig. 3 is a section on line 3-3 in Fig. 2.

Fig. 4 is a horizontal section of a discharge electrode on line 4-4 inFig. 1.

Fig. 5 is a vert-ical section of a tubular or so-called pipe treaterembodying my invention.

Fig. 6 is a section on line- 6-6 in Fig. 5.

Referring to Figs. 1 to 3 the embodiment of my invention shown thereincomprisesa casinfr or conduit 1 having inlet 2 and outlet 3 or the gasto be treated and provided with any desired number of vertical partitionWalls 4 subdividing the interior of said 'conduit into a plurality ofpassages. The walls of the Hue 1 and the partition 4 constitute thecollecting or :so-called passive electrodes and may consist of anysuitable semi-conducting or high resistance material presentingsufficient conductivity for carrying the precipitating current butpresenting suiiiciently high resistance to `reduce the tendency toexcessive concentration of the precipitating current at a point orpoints of said electrodes. For this' purpose said electrode members 1and 4 may consist of reenforced concrete or similar material, consistingfor example of concrete walls of Portland cement and suitable aggregateand having metal re-enforcing bars or rods 5y which are arranged inspaced parallelism, for example vertically, andgare connected togetherand to ground by wires or conductors 6. Suitable means such as hopper 7may be provided below the flue 1 for receiving the material precipitatedupon the collecting electrodes and removed therefrom by the action 'of'gravity or in any other suitable manner.

`Within the flue spaces between the walls 1 Vand theA artition means 4are provided discharge e ectrodes 8 consisting for example of 'ventingcracking of said material.

metal Wires, rods, or other conductors 8 of relatively" smallcross-section and having continuous and substantially smooth-surfacedcoatings or coverings 9\ of suitable semi-conducting material at allportions thereof opposite the collecting electrodes.

Said discharge electrodes may be suspended from a supporting frame 10mounted on insulators 11: in the usual manner of electricalprecipitators of this character. Said semiconducting coatings mayconsist for exam le of Portland cement concrete, prefera ly made up witha suitable amountof fine sand but with little or no coarse aggregate, orother suitable cementitious material with or Without asbestos or otherfibrous material incorporated therein for the purpose of pre- Othersemi-conducting materials may also be used for this purpose, forexample, enamels containing suflicient incorporated conducting materialto rendei t-he same semi-conducting, said conducting material consistingfor exanple of conducting metal oxides, finely divi ed metals, carbon,etc. The term semiconducting as used herein is applied to the generalclassiofmaterials Whose electrical conductivity is intermediate betweenthat of Substances which are generally considered good conductors, suchas metals, carbon, etc., and thaty of materials which are generallyconsidered nonconductors, such as glass,

- porcelain, quartz, rubber, etc. For the purpose of my invention Iprefer to lform the` semi-conducting coatings or covers 9 of materialshaving an electrical conductivity, ,at

temperatures not exceeding 200 C., between the order of 102 and 10reciprocal ohms er centimeter cube. Materials having an e ectricalconductivity within this range' are adapted to permit the flow ofsufficient electrical current to effect electrical precipitation and atthe same time to prevent excessive flow of current to any part of theprecipitator. The wires or rods 8 may be of any suitable small diameter,for example 11g inchv to l@ inch or larger and the thickness of thesemi-conducting' coatings 9 mayl be varied, according to the materialused vand the conductance desired, for example from a` mere film in thecase of enamels to a'thickness of l@ inch or more in the case ofcementitious materials.

The term substantially smooth-surfaced as applied to the semi-conductingcoatings is not to be understood as precluding any minor roughness orunevenness which is inherent in the material used in such coating. Suchcoating should, however, as shown for example in Figs. 1 and 4, be ofsubstantially uniform thickness, with a surface as smooth as it ispracticable to obtain with the material used. Any minor roughnesses orprotuberences which may occur are to be considered as "merely incidentaland unavoidable andare not relied upon according to this invention forfacilitating electrical discharge therefrom. This construction istherefore to be distinguished from certain types of previously useddischarge electrodes which comprise a conducting member with pro]ectingfragments of non-conducting material secured thereto, in which case theprojecting points or edges of the non-conducting material wereintentionally provided for the purpose of facilitating electricaldischarge therefrom.

I prefer to arrange the discharge electrodes 8 in parallel-relation tothe re-enforcements 5 in the collecting electrodes and opposite thespaces between such re-enforcements so as to equalize the electricalfield intensity throughout the surface of the collecting electrodes asset forth in my patent above referred to.

The operation of this form of the'invention is as follows: V

A high potential difference, preferably unidirectional, is applied tothe electrodes for example by connecting the high tension systemcarrying the discharge electrodes 8 through Wire 12 to any suitablesource of high tension rectified alternating current for example in themanner set forth in U. S. Patent to F.,G. Cottrell, No. 895,729, datedAugust 11,1908. A strong electric field is thus producedtbetween thesurfaces of the semi-conducting coatings 9 of the discharge vcollectingelectrodes 1 and 4 with the result that an electrical discharge takes-place mainly from the discharge electrodes on account of thevrelatively limited cross-section and correspondingly sharp curvaturethereof. Such electrical discharge takes place from the surface of thesemi-conducting coating 9 of each discharge electrode and the currentmust therefore pass through said semi-conducting material, whichprevents undue concentration of the electrical field at any portion ofsuch surface. This effect is further increased in this case by thesemiconducting character of the collecting electrodes 1 and 4, with theresult that a very uniform distribution of electrical discharge, corona,or ionization is maintained throughoutthe body of gas passing betweenthe electrodes and a more rapid, complete, and uniform electrical chargeof the suspended particles in they gas is secured with .resulting rapidand com lete electrical precipitation of such suspen edparticles. Suchprecipitation takes place in the usual manner of electricalprecipitation operations, by translation of the electrically chargedparticles under the action of the electrical field'toward the collectingelectrode, it being understood that the particles will be electricallycharged in the same sense as the discharge electrodes and will thereforebe forced by the action of the electrical field away from the dischargeelectrodes and towards the collecting electrodes. Due lto the uniformdistribution of the electrical field, and the prevention of arcing anddisruptive discharge brought about by the semi-conducting coating on thedischarge electrodes and the semi-conducting nature of the collectingelectrodes, a very high potential difference may be safely maintainedbetween the \electrodes without danger of producing disruptivedischarge.

The discharge electrode provided .with a semi-conducting coatingaccording to my invention may also be used in connection with metallicor conducting collecting electrodes.

As an .example of this I have shown in igs.` -5 and 6 a precipitator ofthe tubular or pipe type comprising a vertical tubular casing 13 formedfor example of steel, cast iron, or other suitable' metal and adischarge electrode 14 mounted so .asnto extend axially Within thetubular casing 13 and consisting of a Wire, smallrodor other conductor14; provided with coating or covering 15 of semiconducting material'such as a semi-conducting enamel of the type above described.

Said discharge electrode may be mounted on Vsuitable insulating means 16and may be provided at its lower end with tensioning means such asweight 17. .The discharge and collecting electrodes are in this caseprovided with electrical connections similar to those shown in Figs. 1lto 3 and the operation of this form of my invention is substantiallythe same as that above described. 'It will of course be understood thatin practice any suitable number of vertical flues or pipes 13 may beconnected in parallel arrangement in the usual manner of multiple pipeelectrical precipitators, a discharge electrode 14 provided with asemi-conducting coating being arranged within each of said fines.

I claim:

1. In apparatus for electrical. precipitation of suspended particlesfrom gases, a discharge electrode comprising a conducting member ,and acontinuous coating of semiconducting material surrounding saidconducting member.

2. In apparatus for electrical precipitation of suspended particles fromgases a dischar e electrode comprising a conducting mem er, and acontinuous coating of semiconducting material surrounding. saidconducting member, said semi-conducting material having an electricalconductivity, at temperatures not exceeding 200o C., between the orderof 1072 and 10@ reciprocal ohmsv trode and means for maintaining a highpotential difference between said discharge andV collecting electrodes.

4. An .apparatus as set forth in claim 3, said collecting electrodebeing of semi-conducting material so as to present high 4resistancethroughout its area.

5. In apparatus for .electrical precipita- -tion of suspended particlesfrom gases, a

discharge electrode comprising a conducting member and a continuouscoating of semiconducting cementitious material surrounding saidconducting member.

6. In apparatus for electrical precipitation of suspended articles fromgases, a discharge electro e. comprising-a conducting member andac'ntinuous and substantially gli smooth-surfaced l coating ofsemi-conducting material surrounding said conducting mem ber.

,In testimony whereof I have hereunto sub'- scribed my name this v11thday of September, 1925.

'EVALD ANDERSON.

